Impact of grazing on litter decomposition and nutrient availability in a grass-encroached Scots pine forest

In a grass-encroached Scots pine forest, grazing was found to reduce the above ground and below ground biomass production of Deschampsia flexuosa. This led to a reduction in the input of litter and nutrients to the soil (Smit and Kooijman, 2001). Its consequences for decomposition rates and nutrient availability were studied in a 7-year experiment with two grazing intensities and non-grazed control in a pine stand. Decomposition of fresh litter (needles and grass leaves) was not different between grazed and non-grazed sites. There were differences between nutrients in turnover rates, which may be important as to which nutrient becomes (the most) limiting. The net release of N was relatively slow and a 30% decrease in N-availability, as suggested by a decrease in N-mineralisation and BaCl2-extractable ammonium, did not occur before 7 years of grazing. In contrast, K leached very rapidly from dying and dead needles and grass leaves. Potassium availability in the soil was reduced already after a few years of grazing. Calcium levels in the soil increased due to the increasing importance of Ca-rich pine needles and because Ca is preferentially bound to the soil exchange complex. The reduced availability of both N and K may at least partly explain the reduced biomass production of the grass vegetation. (C) 2002 Elsevier Science B.V. All rights reserved.